This invention relates to a method for protecting digital data from unauthorized mass duplication. More specifically, this invention relates to a method for copy protecting digital video signals recorded on a storage medium, such as a compact disc.
The recent development of consumer electronics incorporating devices for the reproduction of digitally-recorded audio and video data has resulted in the corresponding development of a vast consumer market for digitally-recorded media. Such digitally-recorded media are available in a number of different forms, including optical disc, magnetic disc, magneto-optical disc, magnetic tape, cartridge, and the like. Commonly, many of these forms of digitally-recorded media are available for sale or rental. Additionally, consumers may access and retrieve for storage digital audio and video data from cable systems, computer networks, satellite transmission systems, and the like.
Generally, prerecorded digital media contain a complete and virtually error-free duplicate of original data reproduced from an original digital master recording. As is well known in the art, digital data stored on a prerecorded digital medium may be reproduced many times without significantly affecting the quality of the stored data. Hence, a prerecorded digital medium may itself be utilized as a template from which many additional copies of digital data may be reproduced and recorded on other digital media.
The ease with which such reproduction and recording operations may occur and the high quality of the resulting recordings has facilitated the development of significant efforts to produce and distribute counterfeit prerecorded digital media. Although counterfeiting may occur in small volumes through the use of consumer recording/reproducing devices, a more significant problem has arisen from the use of mass production recording devices. In the optical disc industry, optical discs are mass produced with a formatting device, termed a "formatter", which reproduces digital data from a master recording and records the reproduced data onto an "original" disc. A stamping template, "stamper", is made from this "original" disc. The "stamper" thus created, may then be used to produce large numbers of optical discs, e.g. ROM discs, bearing the original digital data. Hereinbelow, the mass produced optical discs will be referred to as "retail discs."
At present, it is difficult, if not impossible, for an optical disc producer to determine the authenticity of or legal title to a particular master version of digital data provided by a third party. For example, a counterfeiter may bring an illegally obtained master recording, "original" disc, or "stamper", or even a retail disc, to an optical disc producer for mass reproduction of the recorded digital data. Unable to verify the authenticity of or legal title to the digital data supplied by the counterfeiter, the optical disc producer may unwittingly mass produce optical discs bearing the counterfeiter's digital data. Such counterfeit optical discs have the potential to be indistinguishable from retail discs produced under proper authority from legal master recordings.